This invention relates to an image recording apparatus such as an optical printer, a copying machine or the like for recording an image onto a photosensitive recording medium by a slit-scanning exposure system.
Referring to FIG. 1 of the drawings, there is schematically shown a usual or general copying machine for copying image information on an original to a photosensitive recording medium. The copying machine comprises a transparent glass platen 51 movable in a direction indicated by an arrow A. An original 52 having carried thereon image information is placed upon the platen 51. Light from a light source 53 scans the information side of the original 52, while the original 52 as well as the platen 51 is moved in the arrowed direction A. Light reflected by the original 51 is directed toward a photo-sensitive recording medium 54 transported in a direction indicated by an arrow B, so that the recording medium 54 is exposed to the light through a slit 57. The recording medium 54 is then developed by a pressure developing unit 55. For the arrangement illustrated in FIG. 1, it is required that the recording medium 54 is exposed to the light while being maintained horizontal. To this end, in general, a table 56 is provided for enabling the recording medium 54 to rest upon an upper surface of the table 56. The recording medium 54 moves in sliding contact with the upper surface of the table 56.
In the above-described conventional copying machine, it is needless to say that, when a photosensitive recording medium low in photo-sensitivity is used, power of the light source 53 is raised to increase the light quantity to which the recording medium is exposed. If the increased light quantity is concentrated into the slit 57 narrow in width, however, there is such an anxiety that a bad influence is exerted upon the recording medium. Thus, attention is required to be paid to enlarge the width of the slit 57 so as to prevent the light quantity per unit area from increasing excessively.
When the width of the slit 57 is enlarged, however, it is required to considerably enhance the accuracy of the delivery speed at which the original 52 and the recording medium 54 are moved in synchronism with each other. In addition, extremely high accuracy is required for attachment and arrangement of reflecting mirrors, a lens system and so on for leading the light from the light source 53 to a predetermined line on the original 52 and for leading the reflected light from the original 52 to the recording medium 54. Thus, the arrangement of the conventional copying machine is disadvantageous particularly in recording of an image at high resolution.
Further, there are a case where a user desires to quicken the copying speed at normal resolution at which the slit width is normal and the scanning speed is normal, and a case where the user desires to take a copy at high resolution though the copying speed may be slow at which the slit width is small and the scanning speed is slow. It is impossible for the conventional copying machine, however, to fulfill such user's wishes simply.